In recent years, the LED technology has big progress in the efficiency of brightness, and many applications for displays appear continuously. Also, the optical proximity sensor (OPS) is commonly used in wireless communications, bio-molecular sciences, environmental monitoring, and displays. The OPS is developed based on the light signal received by the photo-detector (PD) via the reflections of the measured object. The PD transfers the light signal to the electrical signal. By detecting the intensity of the electrical signal, the OPS can calculate the distance of measured object.
The conventional OPS is used mostly for switches; however, there are limited applications for OPS. Also, the OPS needs to comply with the specific color or shape to effectively detect the object, and it is easily affected by the ambient light or the dark current, which results in a wrong detection. In addition, the OPS has at most two-dimensional detection range (i.e. single plane detection range). Thus, it can not do a three-dimensional coordinate sensing of an object.